1. Field of the Invention
The present invention relates to a liquid container capable of accommodating pigment ink therein and to an inkjet recording apparatus that supplies the ink from the liquid container to a recording head via a tube or another member.
2. Description of the Related Art
Inkjet printing is a printing method that forms an image by spraying a single-color ink or inks of different colors prepared for color printing onto a print medium (e.g., paper or transparency film). A recording apparatus using this inkjet printing method includes a liquid container (ink tank) as a cartridge in the vicinity of a print head on a carriage, the liquid container being integral with or separate from the print head. When the ink has run out in the liquid container, the cartridge is replaced with a new one to restock ink. This cartridge replacement type is the most popular inkjet printer type.
However, the cartridge replacement type has a limitation of providing an ink tank on a carriage up to a certain size. If a large ink tank is provided to reduce the frequency of replacement of the ink tank, a space occupied by the ink tank is significantly large. This increases the size of a recording apparatus and the power required to move the carriage. As a result, a very large power source is required, and other various problems arise.
Thus, in a large recording apparatus that is called a wide format printer, an ink tank having sufficient capacity is detachably mounted on a securing point of the printer. In that printer, supplying ink to a recording head on a carriage through a tube connected to the recording head using a pump is a typical system.
Business-grade recording apparatuses such as wide format printers need to use pigment ink with excellent resistances to water and light. However, the pigment ink has a problem in which pigment precipitates on the bottom of the ink tank when it is left standing for a long time and thus ink concentration varies depending on the location within the ink tank. In particular, variations in concentration are apt to increase with the volume of ink within the ink tank and with the height relative to the base area. For a recording apparatus such as a wide format printer, a significantly large ink tank capacity is desired in order to reduce running costs, and in the case of pigment ink, concentration variations are a very serious problem that might decrease image quality.
One known approach to the problem of concentration variations is an arrangement discussed in U.S. Pat. No. 6,824,258. In this arrangement, the bottom of an ink tank is provided with a first connection port for connection with a main body of an apparatus and for use in supplying ink to a recording head and a second connection port for connection with an air communication chamber and for use in introducing air from atmosphere, these two connection ports are disposed adjacent to an end of the bottom of the ink tank, and the inside of the ink tank is agitated by the introduction of bubbles from the communication unit connected to the atmosphere.
Another known approach is an arrangement discussed in Japanese Patent Laid-Open No. 2002-019137 in which the inside of an ink tank is agitated by the introduction and ejection of ink using a pump.
A known method of agitating precipitated ink using bubbles is described with reference to FIGS. 9 to 11, and a known method of agitating precipitated ink using the introduction and ejection of ink is described with reference to FIG. 12.
FIG. 9 is a schematic diagram of an ink supply route for explaining a known method of agitating precipitated ink using bubbles.
An ink tank 1 detachably mounted on a main body of an inkjet recording apparatus includes two independent connection ports for connection with the main body at the bottom. Each of the two connection ports is formed from a sealant. The inkjet recording apparatus includes connection ports 5 (5a and 5b), each of which is formed from a hollow tube. The first connection port 5a is adjacent to an end of the ink tank 1 and communicates with a recording head 2 through a supply tube 4. Ink is supplied from the ink tank 1 to the recording head 2 through the first connection port 5a. An ink supply valve 3 is located within the ink supply route. Opening and closing the ink supply valve 3 enables and disables the supply of ink to the recording head 2. The second connection port 5b communicates with an air communication chamber 6. Air introduced from an air communication port 7 is introduced into the ink tank 1 through the second connection port 5b. Ink is ejected from the ink tank 1 and the internal pressure of the ink tank 1 is thus reduced, thereby introducing air into the ink tank 1 from the air communication port 7 and thus relieving the internal pressure of the ink tank 1. When the temperature inside the ink tank 1 is increased, air inside the ink tank 1 is expanded, the internal pressure of the ink tank 1 is increased, and ink is ejected from the second connection port 5b to the air communication chamber 6. The air communication chamber 6 has a capacity corresponding to the expansion of air inside the ink tank 1. When ink is discharged from the recording head 2 and consumed, ink stored in the air communication chamber 6 is first consumed, and ink in the ink tank 1 is then consumed.
FIGS. 10A to 10C illustrate how a uniform concentration distribution of pigment ink in the ink tank at the initial stage is changed after the ink tank is left standing.
FIGS. 10A and 10B illustrate how a uniform concentration distribution of ink in the ink tank at the time of attachment of the ink tank is changed after the ink tank is left standing. FIG. 10C is a diagram for explaining the structure of concentration distribution. As shown in FIG. 10B, when the ink tank 1 which stores pigment ink is left standing for a predetermined period of time, an ink ingredient distributed in the ink (e.g., pigment) precipitates downward vertically with time. As a result, the concentration of pigment ink at a lower part of the ink tank 1 is increased, and the concentration of pigment ink at an upper part of the ink tank 1 is reduced accordingly. At an intermediate part of the ink tank 1, an appropriate concentration of pigment ink is formed. Therefore, the uniform concentration is changed to a three-layer concentration distribution. As the time for which the ink tank is left standing is increased, the concentration of highly concentrated ink at the lower part of the ink tank 1 is increased, and the amount thereof is also increased. The concentration at the upper part is reduced accordingly. As the height of the ink tank 1 relative to the base area is increased, the concentration and the amount of the highly concentrated ink at the lower part of the ink tank 1 caused by being left standing is increased.
When air is introduced into the ink tank 1, the air forms bubbles, and the bubbles flow toward the top of the ink tank 1 due to their buoyancy. Since the second connection port (air introduction port) 5b of the ink tank 1 is disposed adjacent to an end of the bottom of the ink tank 1, a flow of ink is generated in the ink tank 1, as shown in FIG. 11, and the ink inside the ink tank 1 with the three-layer concentration distribution is thus agitated. As a result, the concentration is rendered uniform.
FIG. 12 is a diagram for explaining a method of agitating precipitated ink by causing ink to be introduced into and ejected from an ink tank and thus producing a flow of ink inside the ink tank using a pump.
An ink tank 1 detachably mounted on a main body of an inkjet recording apparatus includes three independent connection ports 5a, 5b, and 5c for connection with the main body at the bottom. Each of the three connection ports is formed from a sealant. The inkjet recording apparatus includes connection ports 5a, 5b, and 5c, each of which is formed from a hollow tube. The first connection port 5a communicates with a recording head 2 via a supply tube 4 and allows ink to be supplied to the recording head 2. The second connection port 5b communicates with an air communication port 7 and allows air introduced from the air communication port 7 to be introduced into the ink tank 1. The third connection port 5c communicates with a pump 400 constructed of a diaphragm and allows ink to be introduced into the ink tank 1 through an ink path 325 and ejected from the ink tank 1 by the driving of the pump 400. Ink flowing in and out of the ink tank 1 changes air pressure within the ink tank 1. As a result, ink is extruded into the air communication port 7 from the second connection port 5b, which is connected to the air communication port 7. During this time, the ink does not virtually flow toward the recording head 2 because channel resistance is large. Ink flowing in and out of the ink tank 1 produces a flow within the ink tank 1, thus allowing precipitated ink to be agitated.
However, for the exemplary agitation method using bubbles described above, if ink is not consumed, air is not introduced into the ink tank and thus agitation effect is not obtained. Therefore, to achieve an increased effect of agitation, a problem arises in which a large amount of ink has to be wasted.
Additionally, because highly concentrated ink is first supplied toward the recording head, an image quality with uniform concentration cannot be obtained unless all the highly concentrated ink is discarded. In this case, a problem arises in which the concentration of ink remaining in the ink tank after the ink is agitated is smaller than the previous concentration.
For the exemplary agitation method by producing a flow of ink within the ink tank, it is necessary to change the amount of ink flowing into and out of the ink tank depending on the amount of ink within the ink tank. Therefore, if the amount of ink is large, it is necessary to have a large amount of ink flowing in and out of the ink tank. This requires not only a large space for holding a large amount of ink at an air communication side but also a large power source for driving a pump. As a result, a problem arises as to the size of the main body of the apparatus and the cost.
The inventor of the present invention conducted an experiment on agitation of the inside of an ink tank having a base area of approximately 60 mm×24 mm and a capacity of 130 ml by only introduction and ejection of ink. The result shows that the amount of ink flowing in and out of the ink tank required to agitate ink within the ink tank is approximately 10 ml, and a very large pump structure and a very large power source are needed.